For protection of IC (integrated circuit)-based devices, resin packaging is adopted using a variety of resins, mostly epoxy resins. With a recent trend towards miniaturized and light-weight devices, the IC mounting method prevailingly uses the so-called surface mounting technique, which involves a process of mounting devices such as ICs to a substrate and packaging with a liquid resin (that is, an under-fill process).
Such an under-fill process is an approach to solving problems with thermal/mechanical fatigue, and more specifically, by injecting inorganic particles into a high-adhesiveness polymer material such as an epoxy resin to have a value approximating the thermal expansion coefficient of the solder and then applying the polymer material in a gap between the chip and the printed circuit board. The composite polymer material containing inorganic particles as used in this process is called an “under-fill material”.
General under-fill materials are in a liquid state with high fluidity, potentially leaking out on an undesired region and thus causing unwanted contamination, and consequently defective products, or there is difficulty in implementing the high-density mounting technique. To avoid this problem, a method of placing a fence-like dam encompassing the devices has been used.
The conventional dams are formed mostly by using a laminar material formed by punching or a liquid solder resist (e.g., Japanese Patent Laid-Open Publication No. 1996-325476, etc.). However, the conventional dam formation method using a liquid solder resist encounters some problems such as an extremely wide deviation of thickness to implement high-density mounting of ICs, consequently causing leaks of an adhesive (liquid sealant), and a further difficulty of uniformly forming a dam in the case of micronization to a thickness at a micrometer (μm) level.
To solve the problem with the dam formation method using a liquid solder resist, a method of using a dry film solder resist has been suggested. For example, JP No. 1996-097841 or U.S. Patent No. 2010-0116534 discloses a method of forming a dam for preventing the flow of under-fill using a dry film resist. However, the conventional methods are hard to apply in high-density ICs due to some limitations in micronizing of the thickness of the dam, resulting in a failure to form a dam having at least a predetermined height or formation of an extremely uneven dam, particularly in the case of realizing a small thickness.